Are you sure it couldn't be explained by cultural changes? Perhaps the numbers were always there, but higher cultural tolerance has simply brought more out of the closet? At the very least I would expect that to be a contributing factor.
I remember reading about how the increase in mental illness could just be that we are better at diagnosing and recognizing them (and lazy doctors who would rather just prescribe something for your "depression").
No I'm not sure, nor is anyone. But having 1.4% of boomers and 7.3% of millennials identifying as LGBT is a _massive_ difference. Homosexuality is something that by all indications causes incredible mental anguish by suppressing, and from what we understand doesn't really change over a lifetime. Wouldn't we see a massively large number of older people coming out of the closet? Would it really be surprising if endocrine disruptors could have such a massive impact?
I'm not married to either reason, but I'm just feeling very skeptical about your assumption.
A) I don't think we would see a massive number of older people coming out of the closet, because this culture change is generational. Most of your peers aren't going to change their minds just because a younger generation is more tolerant. It's the same reason my 100 year old (really!) grandmother may still use the occasional racial slur. I definitely think there's more peer friction for an older LBGT individual than a younger one.
B) I don't think these numbers are actually out of line with the impact of cultural change.
C) Base on your linked datas, religion may also be a factor. Given that religion is on the decline in the US, especially among millennials, I wouldn't rule that out as a factor either.
It's probably a combination of factors as usual, and maybe endocrine disruptors is one of them.
I remember reading about how the increase in mental illness could just be that we are better at diagnosing and recognizing them (and lazy doctors who would rather just prescribe something for your "depression").